Effect of Phase Transformation of Sputtered Hfo2 by Post Annealing Treatment on the Performance of A-Sizo Thin Film Transistor

The effect of post annealing treatment on the phase transformation and the electrical properties of the sputtered HfO2 is investigated. As-deposited HfO2 films were annealed at 200 and 400[[EQUATION]]C in ambient conditions. Film annealed at 200[[EQUATION]]C retains its amorphous nature however, upon annealing at 400[[EQUATION]]C, it crystallizes into the monoclinic structure. Amorphous films exhibit a bandgap of g 5.8 eV, higher than the bandgap of the monoclinic film ([[EQUATION]] 5.65 eV). Theelectrical characteristics of the Metal-Insulator-Metal devices reveal a nonlinear capacitance with respect to the voltage. The non-linearity is predominant in the as deposited film due to the charge trapping/detrapping led by oxygen vacancy related defects during the deposition. The nonlinearity reduces with annealing temperature due to excess Hf-O bond formation at elevated temperatures. The dielectric constant of the as deposited, 200, and 400[[EQUATION]]C annealed films were estimated as 22.35, 22.64, and 20.57, respectively. The increment in the dielectric constant at 200[[EQUATION]]C is due to its amorphous phase and reduced defects. The a-SIZO transistors fabricated using the as deposited and annealed HfO2 show almost similar threshold voltage of [[EQUATION]] -1 V. The transistor with HfO2 annealed at 200[[EQUATION]]C shows the highest on current (1.04 [[EQUATION]]10*6 A) followed by as deposited as deposited (6.82 [[EQUATION]] 10-7 A) and 400[[EQUATION]]C device (5.86 [[EQUATION]] 10-7 A), respectively. Moreover, the interface state density increases monotonically from 3.98 [[EQUATION]] 1012 to 1.11 [[EQUATION]] 1013 cm-2 for as deposited and 400[[EQUATION]]C devices, respectively. The increment in the interface state density is due to the grain boundary formation due to the crystallization of HfO2